The short answer
U3 means the cooking element has overheated and switched off to protect the cooktop, as the table records. The heat here is at the surface rather than in the electronics: something on top of the glass got hotter than the design allows. Take the pan off, let the zone cool, and look at what you were cooking with.
Code table
Reference| code | meaning | owner-checkable |
|---|---|---|
| U3 | The cooking element has overheated and has switched off to protect the cooktop. | yes |
| U2 | The cooking element has overheated and has switched off to protect the cooktop. | see page |
| U400 | The supply voltage is incorrect. It is outside the normal operating range. | see page |
What you observe
- One zone shuts off mid-cook while others continue — The protection is local to the zone that overheated.
- The zone works again once it is cold — Recovery from cold is what marks a protection rather than a failure.
- NEAR MISS — the zone never heats at all — A zone dead from cold is a different fault entirely.
Likeliest causes first
- An empty, dry or very thin pan — First by a distance: with nothing absorbing the energy, the surface temperature runs away in seconds rather than minutes.
- A warped or undersized pan base — Second: poor contact concentrates heat in one spot of the glass instead of spreading it into the food.
- A sensor or control fault in that zone — Last: genuine hardware failure, suspected only when the cutout happens with normal cookware and normal food.
Check in this order
- Remove the pan and let the zone go cold — Never pour water on hot glass; let it cool on its own.
- Look at the base of the pan you were using — Warping, a small base or a very thin base explains most of these.
- Repeat with a known-good pan and food in it — If it behaves, the cookware was the cause and nothing is broken.
Owner-safe steps
- Take the pan off and let the zone cool untouched — The protection releases itself once the surface is back in range.
About 30 min
- Check the pan base is flat and matched to the zone — A base that rocks or overhangs heats the glass rather than the food.
About 10 min
- STOP HERE — anything under the glass is a service job — The surface is bonded and is not lifted by an owner.
Safety first
Safety
Unplug the appliance or switch off its breaker before removing any panel — a capacitor can hold a charge after the power is off. A cooktop holds charge in its filter capacitors after the supply is cut, and the glass cracks if it is levered. Work only with the surface cold and the breaker off.
When to call
Call when the zone cuts out with ordinary cookware, food in the pan and a moderate setting, because that is the pattern that points at the sensing rather than the cooking. Mention the pan and the setting when you book — a technician who knows a good pan was used starts in the right place. Do not keep resetting and re-firing the zone: the protection exists because that surface is at risk.
Neighbouring codes — U2 and U400 sit beside U3 and name overlapping hardware, so most checks here carry across. Read the two meanings side by side: where they differ in the part named, the order of the checks changes with them.
What this page does not cover
This page is written for the Bosch cooktop class rather than for one model line, and U3 is read exactly as the shared table records it. If your family or model has its own page, that page is the more specific answer and it is linked below — go there first when your model is named. Left out deliberately: connector positions, wiring colours and part numbers, which are family-specific.
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